WO2008064951A1

WO2008064951A1 - Detector circuit

Info

Publication number: WO2008064951A1
Application number: PCT/EP2007/061011
Authority: WO
Inventors: Wolfgang Krauth; Gerhard Knecht
Original assignee: Robert Bosch Gmbh
Priority date: 2006-12-01
Filing date: 2007-10-16
Publication date: 2008-06-05
Also published as: DE502007004963D1; US20100052586A1; ATE480038T1; EP2100369B1; JP2010511370A; DE102006056852A1; EP2100369A1

Abstract

The invention relates to a detector circuit (1) for detecting a change in voltage at a terminal (A) with respect to a reference potential. The detector circuit comprises an electronic switch with a control terminal, which has a predetermined switching potential at which the switch operates, and with a detection signal output for outputting a detection signal (DS), and a voltage matching circuit, which provides a control potential at the control terminal of the switch which corresponds to a potential of the terminal which has changed by a predetermined, fixed potential absolute value, wherein the predetermined fixed potential absolute value is selected in such a way that the control potential corresponds to the switching potential or approximately to the switching potential when the reference voltage is applied to the terminal in such a way that the change in voltage to be detected causes the switching potential of the electronic switch to be exceeded or undershot.

Description

DETECTOR CIRCUIT

The invention relates to detector circuits, in particular for detecting a voltage change on a coil winding of a drive coil of an electric motor.

In EC motors with sensorless commutation, the rotor position is detected by monitoring the voltage across individual coil windings and determining the instant at which a magnetic pole moving past the coil winding induces a voltage change on a non-driven coil winding.

Usually, a first terminal of a coil winding is fixedly connected to a first supply voltage potential, as is the case for example with an M-circuit of coil windings of an electric motor. A second terminal of the coil winding is connected via a drivable transistor to a second supply voltage potential. In the non-activated state, the second connection is connected to the supply voltage potential only via the coil winding. However, as soon as the coil winding moves over a magnetic pole, a voltage is induced which leads to a voltage change with respect to the supply voltage potential. The voltage change is detected and a detector signal is generated which is used to determine the rotor position. Depending on the specific rotor position, the commutation of the electric motor is performed. Usually, for detecting the voltage change across a coil winding, the potential at the second terminal of the coil winding is reduced by a voltage divider, and with a voltage divider, for example, via a further voltage divider

Supply voltage generated threshold voltage, e.g. by means of a differential amplifier, comparator and the like, in order to detect the time of the voltage change to be detected at the motor winding.

The use of voltage dividers is necessary because in the illustrated example, the voltage change takes place in the range of the supply voltage potential, which is usually outside the common-mode rejection range of the differential amplifier. When voltage dividers are used, however, the tolerances of the resistors used for the voltage dividers have a considerable influence on the generated comparison voltage, in particular if the dividing ratio is large. As a result, the accuracy of the determination of the time of the zero crossing or the pole change of the electric motor deteriorates, whereby the efficiency of the commutation is impaired.

It is an object of the present invention to reduce the sensitivity of the detector circuit with respect to component tolerances, so that the time of the voltage change can be detected more accurately and so that when using the detector circuit in a motor control system, the efficiency of driving an electric motor with sensorless commutation increases can be. These objects are achieved by the detector circuit according to claim 1, as well as by the engine control system and the electric motor system according to the independent claims.

Further advantageous embodiments of the invention are specified in the dependent claims.

According to a first aspect, a detector circuit is provided for detecting a voltage change at a terminal with respect to a reference potential. The detector circuit comprises an electronic switch having a control terminal having a predetermined switching potential at which the switch switches, and a detection signal output for outputting a detection signal. Furthermore, a voltage adjustment circuit is provided which provides a control potential at the control terminal of the switch, which corresponds to a potential of the terminal which has been changed by a predetermined fixed potential amount. The predetermined fixed potential amount is chosen such that the control potential corresponds to the switching potential or approximately the switching potential when the reference voltage at the terminal is applied, so that the voltage change to be detected causes the switching potential of the electronic switch to be exceeded or undershot.

The detector circuit makes it possible to detect a voltage change at a terminal whose potential can also be outside the supply voltage of the detector circuit and to output it as an edge of the detection signal. Furthermore, the use of the voltage adjustment circuit, which applies the voltage to be detected by a fixed (essentially absolute) potential amount to the switching voltage. Threshold of the electronic switch changed, the influence of resistance tolerances reduced.

Furthermore, the voltage adjustment circuit may be formed with a diode connected to the terminal and to the terminal

Control terminal of the electronic switch is directly connected, wherein the predetermined voltage amount corresponds to the diode voltage or the breakdown voltage of the diode, which drops across the diode.

According to a further embodiment, the electronic switch is designed as a transistor circuit having a first transistor whose base terminal corresponds to the control terminal and whose base-emitter voltage when the reference voltage is applied to the terminal substantially to the diode voltage of a base-emitter junction of the first transistor is set, so that the first transistor is just still conductive, wherein the voltage adjustment circuit is formed so that the base-emitter voltage drops when the occurrence of the voltage change to be detected below the diode voltage, so that the first transistor transitions into the blocking state ,

Furthermore, the reference voltage can correspond to a supply voltage potential and the emitter terminal of the first transistor can be connected directly to the supply voltage potential, so that the switching potential is defined as the supply voltage potential changed by the diode voltage of the base-emitter junction.

It can be provided that the voltage matching circuit comprises a second transistor whose collector terminal and base terminal are short-circuited and connected to the Control terminal of the switch are connected so that adjusts a diode voltage of the base-emitter junction of the second transistor between emitter terminal and collector terminal of the second transistor.

Preferably, the first and the second transistor are formed as ientische transistors, wherein the emitter terminal of the second transistor via a Abgriffwiderstand to the terminal and the collector terminal of the second transistor via a further resistor to a further supply voltage potential, wherein the resistance ratio between the Abgriffwiderstand and the further resistance is a maximum of 1:50.

In particular, the first and the second transistor are designed as double transistors in integrated form.

According to a further aspect, a motor control for driving an electric motor with a drive signal is provided. The motor controller comprises a detector circuit for outputting a detection signal indicative of an inductive voltage change of a coil winding of the electric motor, and a commutator circuit for commutating the coil winding of the electric motor depending on the detection signal.

According to a further aspect, an electric motor system is preceded by a motor controller and with an electric motor having at least one coil winding, wherein the coil winding is connected to a first terminal fixed to a supply voltage supply potential, and wherein the terminal of the detector circuit is connected to the second terminal of the coil winding is to detect a voltage induced in the coil winding during operation of the motor. A preferred embodiment of the invention will be explained in more detail with reference to the accompanying drawings. Show it :

Fig. 1 is a circuit diagram of a motor control circuit with a detector circuit according to a first embodiment of the invention; and

Fig. 2 is a circuit diagram of a motor control circuit with a detector circuit according to another embodiment of the invention.

Figure 1 shows a circuit diagram of a motor control circuit with a detector circuit 1 according to a first embodiment of the invention. The detector circuit 1 is connected to a coil winding 2 of a drive coil 5 of an electric motor (not shown) to tap a potential. For the sake of clarity, only one drive coil of the electric motor is shown, which is designed to be bifilar with two coil windings wound in opposite directions. Each coil winding 2 is operated via a suitable switching transistor 3, which is connected in series with the coil winding 2 and is driven by a commutator circuit 4 for operating the motor with a respective drive signal, e.g. with the help of pulse width modulated drive signals. The commutation, i. the switching on and off of the coil windings 2 of the drive coil of the electric motor is effected as a function of the rotor position, speed of the electric motor and other parameters.

In sensorless electric motors, the rotor position is determined by detecting a voltage change in min. At least one of the coil windings, which is caused by a relative movement between the coil winding and a magnetic pole by induction. In the motor topology described above, according to an M-circuit, all the coil windings 2 are connected with their first terminals to a high supply potential V _H. An induced voltage can then be detected as a potential change at a second terminal of the coil winding 2, if the respective coil winding 2 is not driven by the commutator circuit 4 via the corresponding switching transistor. The term "potential" is understood herein to mean voltage potential at a node, while "voltage" refers to the potential difference between two nodes.

Core of the detector circuit 1 represents a transistor circuit with a transistor 7 and with the collector resistors 12 and 13, which are connected in the form of an emitter circuit. In detail, this means that the emitter of the transistor 7, which is formed as a PNP transistor is connected to the high supply voltage potential V _H and the collector of the transistor 7 via a series circuit of the collector resistors 12 and 13 with a low supply voltage potential V _L ,

The emitter circuit is operated as an electronic switch, which is controlled via the base terminal of the transistor 7. To the base terminal of the transistor 7, in a non-induction case in which no voltage is induced in the coil winding 2, a control potential is applied, which operates the transistor 7 at or just above the switching threshold. That is, in the non-induction case, the transistor 7 is just conductive or low impedance or significantly lower resistance than in the locked state. The control potential is generated from the potential at a node A corresponding to the second terminal of the coil winding 2 and a diode 6. The diode 6 is connected in series with another resistor 14 between the node A and the low supply voltage potential V _L. The further resistor 14 makes it possible for a voltage drop in the amount of the diode voltage to be formed across the diode 6. At the cathode of the diode 6, ie at the node between the diode 6 and the further resistor 14, the control potential is tapped. The diode 6 is dimensioned so that a potential is set as a control potential, in which the transistor 7 is just turned on, that is conductive. If a voltage is now induced in the coil winding 2 which causes the potential at the node A to rise, the control potential at the base terminal of the transistor 7 also increases, since the control potential substantially reduces the potential of the diode which is reduced by the diode voltage of the diode 6 second terminal of the coil winding 2 represents. However, even a slight increase in the control potential at the control potential of the transistor 7 has the consequence that the transistor 7 changes from a low-resistance state into a blocking state. Instead of the conventional diode 6, a zener diode may also be provided in the blocking operation in order to reduce the potential at the terminal A by the breakdown voltage, so that the most accurate adaptation of the control potential to the switching threshold can be made.

As already described above, the collector terminal of the transistor 7 is connected to the low supply voltage potential V _L via a series circuit of two collector resistors 12 and 13. At a node B between the two collector resistors 12, 13, the output of the detector Circuit a detection signal DS are tapped, which detects the occurrence of a voltage increase in the coil winding 2 due to induction as described above by a voltage drop is detected in the induction case. When the voltage at the node A rises, a falling edge at the node B results as the detection signal DS.

The detection signal DS can now be connected to an input of a Schmitt trigger 9 or, alternatively, a comparator and the like, in order to further increase the edge steepness and to reduce interference influences, e.g. to reduce to the detection signal DS by crosstalk of the drive signal. Furthermore, an output of the Schmitt trigger 9 can be connected to a filter circuit 10 in order to eliminate disturbing influences due to the timing of the phase voltages by the commutator circuit 4. The filter 10 is designed as a low-pass filter, since the frequency of the voltage inductions in the coil windings is significantly lower than the frequency of the control of the phase voltages by the commutator circuit 4th

The provision of the collector resistors 12 and 13 makes it possible to bring the output voltage of the emitter circuit in a potential range in which the Schmitt trigger 9 is lent lent. In an exemplary embodiment, the supply voltage of the electric motor (V _H - V _L ) can be 12 volts and used as a Schmitt trigger 9 is a standard module that requires a supply voltage of eg 5 volts. Thus, the Schmitt trigger 9 is sensitive only in a voltage range between 0 and 5 volts (eg at about 2.5V), so that brought by means of the collector resistors 12 and 13, the output voltage of the emitter circuit in a working range of the Schmitt trigger 9 can be. If, for example, the supply voltage of the electric motor and the entire voltage detector circuit corresponds to a supply voltage of the Schmitt trigger 9, instead of the collector resistors 12 and 13, for example, only a single collector resistor can be used between the collector terminal of the transistor 7 and the low supply voltage potential V _L Output of the emitter circuit in this case can be tapped directly on the collector of the transistor 7.

Optionally, to protect the detector circuit 1 may be provided two parallel, mutually opposite freewheeling diodes 8, which are provided between the second connection of the coil winding 2 and the high supply voltage potential V _H , so that an induced voltage in the coil winding 2, whose Amount is greater than the diode voltage can be limited by the respective freewheeling diode 8 in both the positive and in the negative direction against the high supply voltage potential V _H.

2, a further embodiment of the invention is shown. Therein, like reference numerals correspond to elements of the same or comparable function.

Since it is difficult in practice, for example when using discrete components, to select the diode 6 in such a way that the transistor 7 is operated close to its switching threshold or directly at its switching threshold, instead of the diode 6 an additional transistor 11 identical to the transistor 7 can be used be provided. In such a case, the identical further transistor 11 is switched as a diode, ie its base connection is directly, preferably directly, connected to its collector terminal. The diode voltage of the diode-connected further transistor 11 and the voltage of the switching threshold of the transistor 7 are thus almost identical.

In order to operate the transistor 7 in the non-induction case in the conductive or in the low-resistance state, a Abgriffwiderstand 15 and the further resistor 14 are provided. The tap resistor 15 is, preferably directly, between the node A, that is, the second terminal of the coil winding 2, and the emitter terminal of the further transistor 11 and the further resistor 14 between the collector terminal of the further transistor 11 and the low supply voltage potential V _L arranged. A current flow from the node A via the tap resistor 15, the further transistor 11 and the further resistor 14 to the low supply voltage potential V _L causes a voltage drop across the tap resistor 15, so that the control potential applied to the base terminal of the transistor 7, is lowered so that the transistor 7 is in the on state. In order not to impair the sensitivity of the voltage detector circuit 1 in that the control potential in the non-induction case is removed too far from the actual switching potential of the transistor 7, the ratio of the tap-off resistor 15 to the further resistor 14 is preferably very small, ie 1:50 and less, especially 1: 100. Preferred values are, for example, for the tap-off resistor 15 in the range of 1 kOhm to 10 kOhm and for the further resistor R2 in the range of lOOkOhm to 500kOhm.

The voltage divider from the collector resistors 12 and 13 adjusts the low measuring range of a downstream comparator or Schmitt trigger 9. However, it is preferable the total resistance of the collector resistors 12, 13 chosen large, since thereby the gain of the emitter circuit formed with the transistor 7 is increased.

In order to ensure that the diode voltages of the base-emitter junction of the transistors 7 and 11 are as identical as possible, the transistors for the detector circuit 1 are preferably designed as a double transistor, wherein the two transistors 7, 11 are integrally formed, so that they are substantially identical in construction and thermal effects largely compensate by the integration.

In the embodiment, the freewheeling diodes 8 are connected between the emitter terminal of the further transistor 11 and the high supply voltage potential V _H.

The detector circuit may also be configured in an analogous manner for detecting a voltage reduction with respect to a low supply voltage potential by forming it inversely with an npn transistor circuit and by interchanging the high and low supply voltage potentials. As a voltage adjustment element for adjusting the potential at terminal A, a DC source, e.g. in the form of a battery and the like.

The detector circuit 1 generates a detection signal DS which, optionally filtered by the Schmitt trigger 9 and the low-pass filter 10, is supplied to the commutator circuit 4, which evaluates the detection signal and can determine therefrom the rotor position, the speed of the motor and other relevant variables ,

Claims

claims

A detector circuit (1) for detecting a voltage change at a terminal (A) with respect to a reference potential, comprising:

an electronic switch having a control terminal which has a predetermined switching potential at which the switch switches, and a detection signal output for outputting a detection signal,

a voltage adjustment circuit that provides a control potential at the control terminal of the switch that corresponds to a potential of the terminal modified by a predetermined fixed potential amount, wherein the predetermined fixed potential amount is selected such that the control potential when the reference voltage is applied to the terminal Switching potential or approximately corresponds to the switching potential, so that the voltage change to be detected causes an exceeding or falling below the switching potential of the electronic switch.

2. detector circuit (1) according to claim 1, wherein the voltage adjustment circuit is formed with a diode (6) det, which is directly connected to the terminal (A) and to the control terminal of the electronic switch, wherein the predetermined voltage amount of the diode voltage or the breakdown voltage of the diode (6) corresponds, which drops across the diode (6).

3. detector circuit (1) according to claim 1, wherein the electronic switch as a transistor circuit with a first transistor (7) is formed, the sisanschluss corresponds to the control terminal and its Base-emitter voltage is set at application of the reference voltage at the terminal substantially to the diode voltage of a base-emitter junction of the first transistor (7), so that the first Transis- tor (7) is still conducting, the Spannungsungsan - Matching circuit is formed so that the base-emitter voltage drops when the voltage change to be detected falls below the diode voltage, so that the first transistor (7) passes into the blocking state.

4. The detector circuit according to claim 2, wherein the reference voltage corresponds to a supply voltage potential and the emitter terminal of the first transistor is directly connected to the supply voltage potential so that the switching potential is changed as that about the diode voltage of the base-emitter junction Supply voltage potential is fixed.

5. detector circuit (1) according to any one of claims 3 and 4, wherein the voltage adjustment circuit comprises a second transistor (11) whose collector terminal and base terminal are short-circuited and connected to the base terminal of the first transistor (7), so that between Emitter terminal and collector terminal of the second transistor (11) sets a diode voltage of the base-emitter junction of the second transistor (11).

6. detector circuit (1) according to claim 5, wherein the first (7) and the second transistor (11) are formed as identical transistors, wherein the emitter terminal of the second transistor (11) via a Abgriffwiderstand (15) with the terminal and the collector terminal of the second transistor (11) via a further resistor (14) with a further supply voltage potential. tential, wherein the resistance ratio between the Abgriffwiderstand (15) and the further resistor (14) is a maximum of 1:50.

7. detector circuit (1) according to claim 6, wherein the first (7) and the second transistor (11) are designed as double transistors in an integrated form.

8. A motor controller for driving an electric motor with a drive signal comprising:

- A detector circuit (1) according to one of the preceding claims for outputting a detection signal indicating an inductive voltage change of a coil winding (2) of the electric motor,

- A commutator circuit (4) for commutating the coil winding (2) of the electric motor depending on the detection signal (DS).

9. Motor controller according to claim 8, wherein at least one of the following elements is provided:

a Schmitt trigger (9) for receiving the detection signal and filtering interference from the detection signal;

- A low-pass filter (10) for filtering interference signals occurring on the detection signal at frequencies of the drive signal generated by the commutator circuit.

10. Elekromotorsystem comprising:

a motor controller according to claim 8 or 9,

- An electric motor with at least one coil winding (2), wherein the coil winding with a first terminal (A) fixedly connected to a Versorgungsspannungspotenti- al, and wherein the connection of the detector circuit (1) to the second terminal of the coil winding (2) is connected to when operating the engine a in the coil winding (2) induced voltage to detect.